Sodium (hereinafter, including natrium) is an essential element for vital functions of all animals, but excess sodium may cause considerable side effects on a living body. Further, the sodium reacts to metal such as iron to promote corrosion of the metal.
For this reason, an existing sodium detector is used to measure and monitor purity of water for a boiler, a pollution level of drinking water, a concentration of sodium in a fluid utilization system, and the like.
In such applications, since the sodium concentration is a relatively high, the existing detector includes a sodium detecting unit that operates at room temperature and a sodium-signal processing circuit having a relatively high noise figure.
However, in the sodium detector according to the related art, there are considerable variations in measurement baseline and a measured concentration of the sodium due to influence of noises and a temperature change of a sodium detecting unit. Such variations pose problems that a measurement range of the concentration and accuracy in measurement are limited when a concentration of a very small amount of sodium in a liquid is measured. Therefore, there is a problem that the existing detector is difficult to accurately measure a very small amount of sodium in a liquid.